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Melanoma 'down there': Why skin cancer can develop in places not exposed to the sun

Melanomas don't always need UV rays to develop, doctors warn.

by Linda Carroll / May.29.2018 / 4:19 PM ET / Source: TODAY

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Katie Gerber wasn’t that worried when her boyfriend pointed out the especially dark mole on her left buttock. It was in a place that wasn’t exposed to the sun and besides, “it was perfectly round and it didn’t have any of the odd edges or any of the other signs that you look for,” she remembered.

Still, to be on the safe side, the 29-year-old made an appointment with her dermatologist to get it checked out. “When it came back as melanoma, it was really jarring,” Gerber, who lives in Los Angeles and is now 39, said.

Katie Gerber's melanoma was caught at an early stage.Katie Gerber

One of the common myths about melanoma is that it’s always the result of sun exposure. While the sun probably plays a role in many cases, experts say some people inherit genes that make them prone to develop this skin cancer without any exposure to the sun’s rays.

“There are people who have the bad luck to inherit a genetic mutation,” said Dr. Laura Ferris, an associate professor of dermatology at the University of Pittsburgh. Scientists have uncovered a number of these mutations and expect to find more, Ferris said.

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More commonly, people seem to inherit a susceptibility that, in conjunction with sun exposure, can lead to melanoma developing, Ferris said. Researchers have found exposure to ultraviolet radiation leads to changes in the skin. “With sophisticated genetic tools, you can see a ‘UV signature’ in the skin around the melanoma,” she explained.

Another issue for some is tanning salons. Gerber did spend some time darkening her skin in a salon when in high school and she wondered if this raised her risk.

The Centers for Disease Control and Prevention reports 7,665 people in the United States were diagnosed with melanoma in 2014, the most recent year these statistics are available for, and 9,324 people died of the disease.

The numbers are on the rise, the CDC notes. Many melanoma deaths could be prevented if people cut back on their sun exposure and used sunscreen more often, according to the CDC.

After her scare with melanoma, which required surgery to remove the mole, Gerber became very vigilant about sunscreen use and started seeing her dermatologist every six months for checkups.

Ferris pointed to a study that scrutinized the impact of sunscreen. Patients were divided into two groups. One was given sunscreen and encouraged to use it. The other was told to just keep on doing what they’d been doing. “The patients who had been assigned to use sunscreen regularly had their risk of melanoma cut in half,” Ferris said.